1. Field of the Invention
This invention relates to a permanent magnet rotor for a dynamoelectric machine and, more particularly, to a permanent magnet rotor having high performance magnets arranged in a specific configuration and having particular utility in a synchronous motor.
2. Description of the Prior Art
U.S. Pat. No. 4,139,790 to Steen discloses a synchronous motor having a permanent magnet rotor in which the magnets are Rare Earth magnets. The magnets are arranged so that adjacent magnets cooperate to provide magnetomotive forces in parallel.
The aforesaid Steen patent states that permanent magnet synchronous motors have been manufactured with the magnets disposed in a rotor with the long dimension radially and magnetized circumferentially so that two magnets act in series to supply the flux for a given pole of the rotor. The aforesaid Steen patent states that this arrangement has the disadvantage of the shaft's having to be non-magnetic to avoid flux leakage from one face of the magnet through the shaft and back to the other face of the magnet. The aforesaid Steen patent also sets forth that flux leakage can have a path from one face of the magnet to the other through a magnetic bridge along the periphery of the rotor, to further bleed away flux from the useful flux crossing the air gap to the stator.
The rotor of the present invention has magnets disposed with the long dimension radially and magnetized circumferentially so that adjacent magnets act in parallel to supply the flux for a given pole of the rotor in its preferred embodiment. The rotor of the present invention uses high performance magnets such as Ceramic, Alinco Rare-Earth. While the shaft must be non-magnetic, this is not deemed to be a disadvantage as set forth in the aforesaid Steen patent because of the increased flux produced by the adjacent magnets acting in parallel rather than in series as in the aforesaid Steen patent.
As to leakage flux along its periphery, the rotor of the present invention is formed with very narrow bridges on its periphery. The bridges are narrow, yet optimized to provide added mechanical strength at higher speeds. By forming the bridges very narrow, they saturate at a very low level of flux to prevent further flux leakage along the periphery of the rotor of the present invention. This is accomplished by forming the rotor laminations very thin at the outer periphery and coating each of the rotor laminations with an insulating material to minimize eddy current losses.
Accordingly, in its preferred embodiment, the rotor of the present invention utilizes high performance magnets such as Rare Earth magnets, for example, in a radial arrangement without having all of the disadvantages set forth in the aforesaid Steen patent. This radial arrangement of the high performance magnets enables an easier and less costly assembly. It also results in a higher flux's being produced from the same size magnets than can be obtained from the magnets in the aforesaid Steen patent in which the magnets produce the magnetomotive forces in series rather than in parallel.
In another form, the rotor of the present invention utilizes barrier means of electrically conducting and non-magnetic material between adjacent radially disposed high performance magnets. The barrier means are equally angularly spaced from each other as are the high performance magnets.
In a further modification, the rotor of the present invention has high performance magnets arranged in a non-radial arrangement in which a magnetic shaft can be employed. In this arrangement, four magnets are utilized per section with the four magnets being divided into two pairs of magnets, with each pair creating a pole producing its own flux.
The rotor is utilized in a synchronous motor with a frame, which is preferably formed of extruded aluminum, so as to remove heat from the motor and make it run cooler to thereby produce a longer motor life. Because of the higher efficiency, there is lower loss and therefore less heat, which enables the motor to run cooler.
In assembling the rotor, the magnets are not magnetized until just before the final assembly of the rotor within the motor. This arrangement reduces the cost, since magnets which are magnetized are difficult to assemble, because of the strong attraction of the magnets to each other.
By forming the rotor of high performance magnets and optimizing the length, the application of accidental higher voltage, leaving the rotor out in the open or exposing magnets to a high temperature will not cause demagnetization. Accordingly, the possiblility of the magnets' becoming demagnetized is virtually eliminated.
The rotor of the present invention may be utilized in various configurations while still employing the same shape and size of each of the magnets. Since magnets of only one size need to be stocked to build various size rotors, this substantially reduces the cost.
The radial arrangement of the magnets not only provides an additive flux from the adjacent magnets to boost the performance, but it also provides a reluctant torque. This further increases the performance.
An object of this invention is to provide a permanent magnet rotor using high performance magnets having a very high immunity to demagnetizing forces.
Another object of this invention is to provide a permanent magnet rotor for a synchronous motor having a relatively low operating current with high efficiency, high power factor, and high pull-out torque.
A further object of this invention is to provide a synchronous motor having a frame of high thermal conductivity.
Still another object of this invention is to provide a method for forming an improved permanent magnet rotor.
A still further object of this invention is to provide a method for forming permanent magnet rotors in which demagnetized magnets are utilized during assembly of the rotor.
Other objects, uses, and advantages of this invention are apparent upon a reading of this description, which proceeds with reference to the drawings forming part thereof.